As a tire pressure monitoring apparatus, a direct type apparatus is widely known (for example, see JP 4175348). The direct type tire pressure monitoring apparatus has multiple transmitters, an antenna and a receiver. Each of the transmitters is directly mounted on a corresponding wheel of a vehicle. Each of the transmitters is equipped with a sensor, such as a pressure sensor. The antenna and the receiver are mounted on a body of the vehicle. When a detection signal is detected by the sensor, the detection signal is transmitted from the transmitter and is received by the receiver via the antenna. Thus, a tire pressure is detected. When the detected tire pressure is lower than an alarm threshold value, the alarm is activated.
The direct type of the tire pressure monitoring apparatus that is operated by a user and has an initialization switch (reset switch) is currently mounted on a vehicle for practical use. The initialization switch is used for initializing the alarm threshold value, and is mounted inside of the vehicle. The initialization switch is coupled with the receiver by a wiring.
In the above-described tire pressure monitoring apparatus, when an adjusted tire pressure is different from a recommended tire pressure, the alarm threshold value is settable according to the regulated tire pressure. For example, when the tire pressure is regulated to be higher than the recommended tire pressure to meet a preference of a user, the alarm threshold value is set according to the regulated tire pressure.
However, in the tire pressure monitoring apparatus equipped with the initialization switch, operation of the initialization switch is necessary for the user in order to initialize a selected threshold value, which can be set to any value. Therefore, the user may feel inconvenienced.
Further, in the tire pressure monitoring apparatus equipped with the initialization switch, the initialization switch and the wiring, which couples the initialization switch to the receiver, need to be mounted for each vehicle. Accordingly, the number of components of the tire pressure monitoring apparatus is increased, and mounting of the tire pressure monitoring apparatus to the vehicle is laborious.